The present invention relates generally to a method and apparatus for predicting loss of signal quality in a mobile communications system and, more particularly, to a method and apparatus for predicting loss of signal quality in response to knowledge of the environment in which the mobile communications system is used and also to adapting the routing, network selection, or other behavior in response to the prediction to improve the signal quality.
As mobile machines capable of operating manually, partially or fully autonomously at work sites are developed, a large amount of up-to-date information is required to coordinate particular tasks and to provide adequate time for the machines to plan their movements. In some situations, multiple pieces of equipment must work cooperatively with one another and information regarding the activity and movement of each machine and other objects in the environment must be communicated. As the work site becomes more complex and more machines are used, an efficient means for receiving and transmitting data among the machines is required. Further, the information that must be communicated is diverse in nature. For example, the system must support prioritized data, giving precedence to data pertaining to mission-critical operations. Some of the operations may be highly interactive, requiring very low system latencies. There is also large variation in bandwidth requirements, from a few bytes per second to hundreds of thousands of bytes per second or more.
Currently, wireless mobile communications systems are configured to switch between routes or networks in response to detection of loss of signal quality. For example, cellular systems switch base stations when the signal level drops below a specified level, such as when a mobile node moves from one base station area to another. In some cases the drop in signal level occurs sufficiently fast that the connection is lost before hand off to another base station can be completed. For example, a communication system for heavy mobile machinery that is operating partially or fully autonomously cannot afford to lose valuable data during this fade out period; quality communications must be maintained at all times. It is ad therefore desirable to have a mobile communication system with means for preventing degradation of communication signals and loss of information. In order to make most efficient use of the bandwidth available, the communication system would ideally have the capability to choose among several overlapping wireless networks for the networks most suited for a particular application. To prevent loss of communication signals, it is also desired to switch base stations or networks immediately before the mobile node moves from one network to another. This requires the ability to predict handoffs before they are forced and inform the network when it is discovered that a handoff is imminent. The ability to predict handoffs must be reliable in a work environment having a large amount of interference due to complex terrain including hills, trenches, pits, and tunnels, and where the machinery is spread over large distances. Radio frequency (RF) wave propagation in regions having irregular terrain and buildings, such as deep trenches, steep hills, and high walls, require factors such as the reflection, diffraction, multi-path, and scattering effects to be taken into account. The signal strength of the RF signals can fluctuate greatly with small movements in such regions. The reliability of the system must be balanced with speed, since a wireless network can typically be made more reliable by adding error checking and correction, at the expense of lower throughput and higher latency.
In traditional hierarchical data networks, such as the Internet, routing protocols are tied to the logical location of the nodes in the network. When a packet is transmitted, it contains the address of the destination host computer in its header. Intermediate nodes that exist in the path between the source and destination examine the address of the destination and make decisions about how to route the packet based upon the network component of this destination address. This allows the intermediate nodes to forward the packet to the network on which the destination host resides without knowing the exact location of the destination host. As the packet travels along the path, the intermediate nodes that are closer to the destination have information about the exact location of the destination and forward the packet accordingly. One advantage of this type of scheme is that a host only needs to know the location of a few networks of nodes instead of the location of every node in the network.
This traditional network assumes that hosts will be stationary. With lightweight and battery powered mobile computers using wireless technology, users may move around while maintaining connectivity. When nodes move away from their xe2x80x9chomexe2x80x9d network, however, the scheme breaks down. For example, when a mobile computer with an address that belongs to network A moves to network B, the packets that are destined for the mobile computer will still be delivered to network A, as indicated by the network component of the address. All packets that were destined to the mobile computer will be lost while the mobile computer is away from its home network. The limitations of the traditional routing scheme restrict the mobility of these computers by confining them to a single network.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.
In one embodiment of the present invention, a method for communicating between a first communication node and a second communication node in an area having a plurality of communication nodes includes generating a propagation model of signals from selected communication nodes in the area. The communication nodes may be fixed or mobile. The propagation model is based on an environmental map that includes the topography of terrain and structures in the area. The propagation model is generated at selected intervals to provide updated information for predicting the quality of communication at a location at a future time. Additionally, the present invention predicts the future location of a mobile communication node based on the speed and direction of travel of the mobile communication nodes. The previous quality of communication at the predicted location of a communication node is also used. The communication signals are then routed through the network in a manner that provides the desired or best available predicted quality of communication.